1. Field of the Invention
The present invention relates to an erecting equal-magnification lens array plate used in image reading devices and image writing devices.
2. Description of the Related Art
Some image reading devices such as scanners are known to use erecting equal-magnification optics. Erecting equal-magnification optics are capable of reducing the size of devices better than reduction optics. In the case of image reading devices, an erecting equal-magnification optical system comprises a linear light source, an erecting equal-magnification lens array, and a linear image sensor.
A rod lens array capable of forming an erect equal-magnification image is used as an erecting equal-magnification lens array in an erecting equal-magnification optical system. Normally, a rod lens array comprises an arrangement of rod lenses in the longitudinal direction (main scanning direction of the image reading device) of the lens array. By increasing the number of rows of rod lenses, the proportion of light transmitted is improved and unevenness in the amount of light transmitted is reduced. Due to cost concerns, it is common to use one or two rows of rod lenses in an array.
Meanwhile, an erecting equal-magnification lens array plate could be formed as a stack of two transparent lens array plates built such that the optical axes of individual convex lenses are aligned, where each transparent lens array plate includes a systematic arrangement of micro-convex lenses on both surfaces of the plate. Since an erecting equal-magnification lens array plate such as this can be formed by, for example, injection molding, an erecting equal-magnification lens array can be manufactured at a relatively low cost.
An erecting equal-magnification lens array plate lacks a wall for ray separation between adjacent lenses. Therefore, there is a problem in that a light ray diagonally incident on an erecting equal-magnification lens array plate travels diagonally inside the plate and enters an adjacent convex lens, creating noise (referred to as ghost noise) as it leaves the plate.
There is known an erecting equal-magnification lens array plate in which a light-shielding member is provided between the two lens array plates in order to reduce ghost noise (see, for example, patent document No. 1).    [patent document No. 1] JP2009-069801
As described in patent document 1, ghost noise can be reduced to a certain extent merely by providing a light-shielding member between the two lens array plates. In order to form an erect equal-magnification image with higher quality, however, it is desirable to further reduce ghost noise.